The objective of this contract is to obtain information on the ability of chemicals under study by the National Toxicology Program to induce chromosomal damage in the bone marrow cells of treated laboratory mice. Specifically, the contract laboratory will conduct mouse bone marrow micronucleus tests on chemicals supplied by the NTP chemical repository using a protocol prescribed by the Program. Results of these tests will be considered along with results. from other genetic toxicity tests to help reach conclusions on the possible carcinogenic and germ cell mutagenic activity of the test chemicals.